1. Field of the Invention
The present invention relates generally to the structure of radially expansible lumenal prostheses, including stents and grafts. More particularly, the present invention relates to the provision of articulation structures for the construction of flexible and pseudo-flexible prostheses and the provision of end structures for the construction of atraumatic prostheses.
Lumenal prostheses are provided for a variety of medical purposes. For example, lumenal stents can be placed in various body lumens, such as blood vessels, and the ureter, urethra, biliary tract, and gastrointestinal tract, for maintaining patency. Such stents are particularly useful for placement in pre-dilated atherosclerotic sites in blood vessels. Lumenal grafts can be placed in blood vessels to provide support in diseased regions, such as abdominal and other aneurysms.
Both stent and graft prostheses must meet certain mechanical criteria to function successfully. In particular, such prostheses should be at least partly flexible over their lengths so that they may be advanced through tortuous body lumens, such as the coronary vasculature. In addition, such prostheses must have sufficient mechanical strength, particularly hoop strength, in order to maintain lumen patency and/or mechanically augment the lumenal wall strength. The ability to meet both of these requirements is severely limited in the case of cylindrical endolumenal prostheses which are delivered in a radially constrained or collapsed configuration. Such prostheses must be radially expanded at a target site within the body lumen, so any adaptations which are intended to enhance flexibility or maintain strength must not interfere with the ability to radially expand.
Prior lumenal prostheses such as stents often have structures which present a substantial risk of injury as they are endolumenally delivered to and/or released at a target site within a patient body lumen. In particular, many vascular stents comprise a plurality of circumferentially spaced-apart cylindrical longitudinal elements which deform circumferentially as the stent is radially expanded. The Palmaz stent described in U.S. Pat. Nos. 5,102,417 and 4,776,337, is typical of such stents. The termini of the longitudinal elements of such stent structures present sharp, crown-like spikes which can injure or traumatize the blood vessel wall as the stent is delivered and/or radially expanded within the blood vessel.
For these reasons, it would be desirable to provide improved cylindrical lumenal prostheses and methods for their endolumenal placement, where the prostheses can flex in their radially constrained or collapsed configuration while they are being delivered to a target site within a body lumen. The prostheses will be radially expansible at the target location, and will preferably retain both their cylindrical configuration and flexibility after expansion. Such prostheses should further have sufficient hoop strength and other mechanical characteristics so that they may effectively function as stents in maintaining lumenal patency and/or grafts in enhancing lumenal wall strength. Such prostheses should also be provided with atraumatic termini in order to minimize the risk of lumenal injury as the prosthesis is delivered and/or radially expanded within the body lumen. Optionally, such atraumatic termini could also act as anchors for maintaining the prosthesis in the body lumen after expansion.
2. Description of the Background Art
Vascular stents comprising multiple segments joined by axial hinge structures are described in U.S. Pat. Nos. 5,195,984; 5,104,404; and 5,102,417 and European Patent Publication EP 540 290. Other stent structures are described in U.S. Pat. No. 5,282,824, European Patent Publication EP 481 365; and Canadian Patent Publication 2,079,944. U.S. Pat. No. 4,776,337 describes the Palmaz stent which consists of multiple longitudinal box elements joined to each other by short circumferentially oriented tabs.